[AuntBee]

Our vet told us that dog sperm can remain viable in the female's system for as long as 9 days, which is why sometimes mothers are "overdue" by dates.

As far as the registration goes, the AKC registration rules read as follows:

XI. MULTIPLE-SIRED LITTERS
Effective September 1, 2000 (and retroactive for 24 months), the AKC will consider the registration of litters with more than one sire, or litters for which the identification of the sire is in question. The registration must be based upon AKC DNA Certification for the sire(s), dam, and all puppies. In addition to the registration fee for each litter, a penalty fee of $200 (per
dam, per whelping) will be charged for litters with more than one sire. This policy is meant to ensure the integrity of the registry and allow for the registration of purebred dogs with DNA certified parentage - it is not
meant to encourage the use of multiple sires.

Their website goes into a bit more detail regarding the DNA aspect of it:

Multiple-Sired Litter Registration

The American Kennel Club allows for the registration of litters with more than one sire. This is effective for litters whelped September 1, 1998 and forward. Parentage must be determined using the AKC's DNA Profile Program prior to registration, and special fees apply. The proper procedure for pursuing the registration of a multiple-sired litter or for any litter with questionable parentage is as follows:

Obtain AKC DNA test kits for all potential sires, dam and all puppies.

Collect and submit the DNA samples for the sires, dam and all puppies. Samples are collected using a painless, non-invasive cheek swab and can be returned via US Mail, Fed Ex, or other express mail.

If the two (or more) possible sires are related (or just have similar genotypes), additional markers may be required to determine correct parentage of one or more pups. In this case, more testing would be required for the sires, dam and the necessary pups. The cost for additional testing is $20 per dog. AKC has been able to determine the correct sire in every such case to date, with the use of additional markers.

Processing usually takes 6 to 8 weeks, but can take longer if some samples contain insufficient amounts of cheek cells to produce a genotype or if extra markers are required.

After the DNA testing is complete, DNA Profiles for each dog tested will be sent to the owner, and there are two options to choose from concerning the parentage evaluation. First, the breeder may utilize the DNA profiles and the accompanying explanatory worksheet to perform the parentage evaluation him/herself. The second option is to complete and submit an AKC Parentage Evaluation Request Form. With the proper signatures, the AKC will evaluate the parentage and report the results in writing, cost is $40.00.

When the correct parentage is determined, submit the appropriate litter registration application. If all puppies are sired by one dog, then a regular AKC Litter Registration Application is used (cost is $25 plus $2 per puppy). If the litter has two or more sires, then the Multiple-Sired Litter Registration Application is used. An additional fee of $200 is required, plus the normal registration fees for each sire/pup combination. For example: a litter with 2 puppies from one sire and 3 puppies from a second sire would therefore cost $200 plus $29 for litter one and $31 for litter two = $260 total. These fees are in addition to the DNA processing costs.

If the second sire is not the same breed as the bitch (part purebred, part mongrel litter), then the purebred pups, and their sire and dam, need be tested. Depending on the breed of the other stud dog, a DNA sample may be required from him, as well. After the DNA results confirm the parentage, a regular AKC Litter Registration Application is used.

The AKC is pleased to present this option to breeders to allow for the registration of these litters where correct parentage can be determined. Please do not hesitate to contact AKC DNA Operations for assistance.